BMW’s approach to the four-door ‘coupe’ design is arguably less elegant than Audi’s but it’s also less aggressive than Benz’s. We’ll leave you to decide which is the better-looking model, but we’re fans of all three from a styling perspective.

Here we’re focusing on the 640d that didn’t join the range until March 2013 and is the joint entry-level model and the most economical of the Gran Coupes.

Its starting price of $184,800 is a fraction higher than the $184,445 six-cylinder petrol 640i. Those desiring V8 power need $238,445 for the 650i or nearly $300K ($299,145) for the flagship M6.

You’d have to be a serious anti-diesel motorist to not choose the 640d over the 640i, especially with both mirroring spec level.

The 3.0-litre six-cylinder twin-turbo diesel’s maximum power output of 230kW is just 5kW short of the 640i’s 3.0-litre six-cylinder turbo petrol – but embarrasses it for torque by a margin of 40 per cent: 630Nm v 450Nm.

It’s not even slower, sharing the 640i’s 0-100km/h acceleration time of 5.4 seconds. Then on official consumption figures, you’ll use 2.2 litres more fuel in the petrol six 6 Series Gran Coupe.

The 640d’s efficiency of 5.7 litres per 100km is so good the BMW also trumps the rival Mercedes CLS350 CDI (6.2L/100km) and Audi A7 3.0 TDI quattro S-tronic (5.9L/100km).

Paddleshift levers behind the steering wheel can be tapped to shuffle between the eight ratios, though the auto has brains as well as speed and seamlessness and, with the engine’s inability to rev like a petrol, they’re arguably a redundant feature on the 640d.

As with most BMWs these days, you can select between different vehicle settings depending on whether the priority is fuel-saving, cruising or sporty driving.

Eco Pro brings a blue illumination to the TFT instrument cluster and will show how many extra kilometres you’re gaining by using that mode, though a throttle pedal resistant to pressure is the downside.

Comfort is a nice middle ground, and Sport, which turns the dials red, is best left for just that.

Even in Sport mode that stiffens the suspension, the BMW 640d Gran Coupe is a touch bouncy over a quick series of undulations on a country road, becoming floaty at times and taking longer than you’d expect to settle.

There’s nothing grand about the car’s low-speed ride, either, with the suspension capable of bumping and thumping around town even in Comfort setting. It’s a notable drawback for what is meant to be a sporty luxury model.

However, if there isn’t enough emphasis on the second part of that tag (at least when it comes to ride comfort), the sports side is better.

The 6 Series Gran Coupe is a long, wide and heavy car but to a certain extent it belies those facts, and doesn’t mind being hustled along a challenging twisty road.

There’s plenty of groaning from the 640d’s outside rear tyres as the car is pushed to its limits of adhesion, but the grip is more than sufficient for most drivers.

The brakes are a great support act with plenty of bite and feel, and the steering, while more GT than sports coupe in its speed, is buttery smooth, accurate and well weighted.

You don’t have the sensation of driving a four-door, either. The driving position is made to feel sporty by being set lower than in a 5 Series (on which the 6 Series models are based) and the high window line. The super-narrow rear window adds to the effect, though it’s also not ideal for vision.

Another welcome distinction from a 5 Series is the twin-cockpit layout of the front cabin.

There’s still the wonderfully intuitive and smartly presented iDrive infotainment system, and it was a welcome change to drive a German press car in Australia where the list of fitted options was dwarfed by the standard gear – and included a no-cost-option M Sport Package bringing sportier trim enhancements for the interior and exterior.

There isn’t a 640d 6 Series Coupe but the 640i version suggests a premium of about $8K for two extra doors.

The answer to whether the Gran Coupe is worth the extra is found inside those rear doors.

An 11cm-longer wheelbase helps to give the Gran version of the two coupes extra legroom – and there’s a button that allows rear passengers to move the front seats forwards or backwards. Then there’s the amount of headroom in the back that gives you the sense you’re sitting in a passenger car with a sloping rear roof rather than a more claustrophic two-door four-seater.

You can sit five in the Gran Coupe, though the middle passenger would be forced to straddle the wide console/transmission tunnel that rises into air vents.

Still, the BMW 640d Gran Coupe slots into a genuine gap between the 5 Series and 6 Series – marrying sedan practicality with coupe sportiness.

However, the shortage of ride comfort isn’t ideal, and even at this price level the BMW looks expensive against its direct rivals, the $159,200 Mercedes-Benz CLS350 CDI and $149,600 Audi A7 3.0 TDI Biturbo Quattro.

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